Electronic appliances are developing rapidly toward miniaturization, low-cost and high-density integration, which leads to lamination and multi-function of sensitive semiconductor ceramic components. 3D integration is the best solution to achieve multi-function and multi-device integration of a passive electronic component in which an inner metal electrode and a ceramic material should be co-fired. The inner metal electrode material tends to be oxidized at high temperature, so that the co-firing process is required to be carried out in a reducing or an inert atmosphere. However, electrical properties of most of the semiconductor ceramics sintered in the above atmosphere tend to be deteriorated or even lost, so that a re-oxidation treatment should be imposed on the co-firing body in air or oxygen at a temperature lower than the sintering temperature to obtain excellent electrical properties, which is known as a method of reduction and re-oxidation. By the above method, a chip component can use base metal for an inner electrode and an effective way is provided for lamination, multi-function and low-cost of ceramic components.
Barium titanate based positive temperature coefficient (PTC) thermistor ceramics and zinc oxide based varistor ceramics are not only two of the most typical sensitive ceramic materials that combine semiconduction of grains with anomalous effects of grain boundaries, but also two of the most widely used semiconductor ceramic materials. Barium titanate-based PTC thermistor ceramics have a significant thermal switching characteristic which can be used as an overload protection device to realize automatic protection and automatic restoration when an abnormal overheating or an abnormal overcurrent occurs. And ZnO-based varistors have an excellent non-linear voltage characteristic, which can provide overvoltage protection for IC devices and electronic circuits so as to prevent damages caused by electrostatic discharge, surges and other impacts by transient currents (such as lightning strikes, etc.). It can be inferred that ZnO varistors and BaTiO3 PTC thermistors are two types of complementary components for circuit protection, and it has a broad application prospect by preparing a composite component combining a thermistor and a varistor taking the advantage of the above two resistors to achieve comprehensive protection of over-voltage and over-current simultaneously. Furthermore, the PTC thermistor can protect the varistor from failure or even a disaster caused by overload (for example, large fluctuation of the voltage, imposing excessive energy on the component, performance deterioration, etc.), which plays an important role in improving reliability and security of electronic devices.
The research of a multi-functional composite chip component combining a thermistor and a varistor can be traced back to 1989. However, there is no breakthrough in the past 20 years. So far, there are only 7 patents about lamination in a total of 95 patents about a composite ceramic component combining a thermistor and a varistor. Each of the patent JP1152704 of Japan Murata in 1989, the Patent KR20060093628 of Korea in 2005, and the patent CN102047353 applied by Germany-based Dehn and Thorne in China in 2005 prepares a composite component combining a thermistor and a varistor by mechanical mounting, which are complexity, high-cost and low reliability.